This invention relates to a video display apparatus for projecting a still picture or a moving picture with a high color reproduction capability.
A video display apparatus of the projection type which uses light emitted from a light source to project and display a still picture or a moving picture upon a screen is conventionally used practically.
Typically, a video display apparatus of the projection type which is conventionally used widely has such a configuration as shown in FIG. 1. Referring to FIG. 1, the video display apparatus of the projection type includes a reflecting plate 100 having a reflecting surface of a shape of a paraboloid of revolution, a light source 101 disposed at a focus position of the reflecting plate 100, an integrator 102, a red separating mirror 103R, a green separating mirror 103G, a reflecting mirror 103B, and a color synthesizing prism 104 having a cubic shape.
The video display apparatus further includes a reflecting mirror 105R for reflecting red light reflected by the red separating mirror 103R so as to be introduced into a predetermined surface 104R of the color synthesizing prism 104, and a reflecting mirror 105B for reflecting blue light reflected by the reflecting mirror 103B so as to be introduced into another surface 104B of the color synthesizing prism 104 parallel to the surface 104R. The color synthesizing prism 104 is disposed such that green light reflected by the green separating mirror 103G is introduced into a surface 104G thereof perpendicular to the surface 104R and the surface 104B. A pair of optical path length adjusting lenses 106 and 107 are disposed between the green separating mirror 103G and the reflecting mirror 103B and between the reflecting mirror 103B and the reflecting mirror 105B, respectively.
The video display apparatus further includes a red light valve 108R interposed between the reflecting mirror 105R and the surface 104R of the color synthesizing prism 104, a red lens 109R interposed between the reflecting mirror 105R and the red light valve 108R, a green light valve 108G interposed between the green separating mirror 103G and the surface 104G of the color synthesizing prism 104, a green lens 109G disposed between the green separating mirror 103G and the green light valve 108G, a blue light valve 108B interposed between the reflecting mirror 105B and the surface 104B of the color synthesizing prism 104, and a blue lens 109B interposed between the reflecting mirror 105B and the blue light valve 108B.
The video display apparatus further includes a projector lens 110 disposed in an opposing relationship to a still further surface of the color synthesizing prism 104 parallel to the surface 104G.
In the conventional video display apparatus having the configuration described above, a white light lamp such as a xenon lamp or a metal halide lamp is used for the light source 101. Light emitted from the light source 101 is reflected by the reflecting plate 100 and is then introduced into the red separating mirror 103R through the integrator 102 after ultraviolet rays and infrared rays are removed from the light by a cut filter apparatus not shown. Of the light introduced into the red separating mirror 103R, a red light component is reflected by the red separating mirror 103R and the reflecting mirror 105R and then passes through the red lens 109R and the red light valve 108R so that it is introduced into the color synthesizing prism 104. The other color light components of the light introduced into the red separating mirror 103R than the red light pass through the red separating mirror 103R and are introduced into the green separating mirror 103G.
Of the light introduced into the green separating mirror 103G, a green light component is reflected by the green separating mirror 103G and introduced into the color synthesizing prism 104 through the green lens 109G and the green light valve 108G. The other color light component of the light introduced into the green separating mirror 103G than the green light passes through the green separating mirror 103G and is introduced into the reflecting mirror 103B through the optical path length adjusting lens 106.
The light introduced into the reflecting mirror 103B, that is, the blue light component, is reflected by the reflecting mirror 103B and passes through the optical path length adjusting lens 107, whereafter it is reflected further by the reflecting mirror 105B and then introduced into the color synthesizing prism 104 through the blue lens 109B and the blue light valve 108B.
The color light components introduced into the color synthesizing prism 104 are synthesized by the color synthesizing prism 104 and projected onto a screen of the transmission type or the reflection type through the projector lens 110.
In the conventional video display apparatus, since single kind of light source is used by itself for the light source 101, wavelengths included in light emitted from the light source 101 are somewhat one-sided, and therefore, it is difficult to obtain a well-balanced light amount ratio of the three color light components separated by the color separating mirrors 103R and 103G and the reflecting mirror 103B. Therefore, it is difficult to augment the color reproducibility of the conventional video display apparatus. Further, since a white light lamp which is used in the conventional video display apparatus exhibits difficulty in adjustment of the brightness with a high degree of accuracy and emits light with a fixed brightness, it is difficult to adjust the brightness for each of the color light components of red, green and blue independently of each other.
Further, in the conventional video display apparatus, a luminous flux emitted from a white light lamp used as the light source 101 has a circular cross section. In contrast, the light valves 108R, 108G and 108B upon which the light is irradiated normally have a rectangular shape. Accordingly, in order to introduce the light uniformly to the light valves 108R, 108G and 108B, the diameter of the luminous flux incident to each light valve is set greater than the length of a diagonal line of each light valve. Consequently, there is a problem that the irradiation efficiency of the light irradiated from the light source 101 is low.
Thus, another video display apparatus has been proposed which uses a plurality of lamps for its light source or a plurality of semiconductor light emitting elements such as light emitting diodes or laser diodes for each of the three primary colors.
FIG. 2 shows an XY chromaticity diagram indicating color reproduction ranges by a phosphor of a CRT (Cathode Ray Tube), a video display apparatus which uses a light emitting diode and a display apparatus of the NTSC (National Television System Committee) system. It can be seen from the XY chromaticity diagram that, where the light emitting diode is used for the light source, the color reproduction range is greater than the color reproduction range of the phosphor of a CRT or a display apparatus of the NTSC system.
However, since rays of light emitted from a plurality of light sources have angles, non-axial light from outside an optical axis is produced. If non-axial light is included in the light emitted from the light sources, it is difficult to irradiate the light uniformly upon a light valve. Further, since the light is irradiated to the outside of the light valve, also the irradiation efficiency of light is deteriorated disadvantageously.
It is an object of the present invention to provide a video display apparatus wherein, where a plurality of kinds of white light lamps or a plurality of semiconductor light emitting elements having a good color purity are used for a light source, light emitted from the light source can be introduced uniformly and efficiently to a light valve.
In order to attain the object of the present invention, there is provided a video display apparatus which includes a light source unit, an integrator, and a light valve. The light source unit includes a plurality of light source sections each including a light source formed from a semiconductor light emitting element or a white light lamp and a coupling optical element for converting light emitted from the light source sections into substantially parallel light, and is operable to condense light from the light source sections having passed through the coupling optical elements at a predetermined focus position on an optical axis of the entire illuminating system. The integrator is disposed at the focus position of the light source unit and uniformizes an intra-plane light intensity distribution of the light emitted from the light source unit. The light valve has a substantially rectangular shape, and the light whose intra-plane light intensity distribution has been uniformed by the integrator is irradiated upon the light valve.
With the video display apparatus, since light emitted from the plurality of light source sections is condensed and introduced into the light valve, when necessary, the number of light source sections can be increased to increase the light amount readily. Further, since light from the plurality of light source sections is condensed at the predetermined focus position on the optical axis of the entire illuminating system and the integrator is disposed at the focus position, the light can be irradiated uniformly upon the light valve, and the light emitted from the light source sections can be introduced efficiently into the light valve.
A well-balanced light amount ratio of the three primary colors can be obtained and adjustment of the brightness can be performed with a high degree of accuracy using a plurality of different types of white light lamps or a plurality of semiconductor light emitting elements of good color impurity. Accordingly, the video display apparatus can be formed so as to exhibit a high brightness, a superior color reproducibility and a high performance.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.